1. Field of the Invention
The present invention relates to a service distribution system and method where an analog multicast service such as a cable television service (CATV) and a digital service, such as the NVOD (Near Video-On-Demand) service, are mixed.
2. Description of the Related Art
Due to advances in multimedia and transmission channel technologies, a technique that mixes a conventional analog multicast service network (such as a cable television (CATV) network) with a digital service (such as Video-On-Demand (VOD), Near-Video-On-Demand (NVOD) etc.), whose signal source is digital, and provides each subscriber with the mixed service, is currently under development. If one of the subscribers requests access to a desired video source, the Video-On-Demand service individually provides that subscriber with signals originating from the requested video source. In the meantime, the Near Video-On-Demand service provides a plurality of subscribers with signals originating from a plurality of video sources in a multicasting manner. Therefore, each of a plurality of subscribers can select a desired video source from the plurality of video sources.
FIG. 1 shows the conventional technique for mixing an analog multicast service network with a digital service.
An analog CATV signal sent from a CATV-HE (CAble Television-Head End) 101 is transmitted to ONUs (Optical Network Units) 102 numbering from 1 to n via analog transmission channels included in respective paths 104 numbering from 1 to n. Each of the ONUs 102 distributes the received analog CATV signal to STBs (Set Top Boxes) 103 respectively installed for the plurality of subscribers using coaxial cables. The configuration described above is that of a conventional analog CATV network.
In the meantime, a digital service signal originating from a digital source, not shown in the attached drawings, for providing a digital service such as VOD service, NVOD service, etc., is transmitted to the ONUs 102 numbering from 1 to n via digital transmission channels included in respective paths 107 numbering from 1 to n, after it is received at an HDT (Host Digital Terminal) 106. In each of the ONUs 102, a modulator 108 modulates the above described digital service signal using a modulation method such as QAM, VSB, etc., and converts the modulated signal into an analog service signal. Then, a mixer (MIX) 105 mixes the analog service signal with the analog CATV signal for distribution to the STBs 103 respectively installed for subscribers using coaxial cables.
For the above described conventional technique, however, the route of the analog transmission channel included in the path 104 for transmitting the analog CATV signal from the CATV-HE 101 to each of the ONUs 102, is completely separate from the route of the digital transmission channel included in the path 107 for transmitting the digital service signal from the HDT 106 to each of the ONUs 102. Accordingly, the paths 104 for the analog transmission channels numbering from 1 to n and the paths 107 for the digital transmission channels numbering from 1 to n should be arranged separately. This causes a first problem, which is proliferation in the amount of equipment required, which becomes large.
Additionally, when a digital multicast service signal such as that for NVOD service, etc. is distributed to each subscriber, an identical digital service signal is distributed in a multicasting manner. Accordingly, the identical digital service signal is distributed from the HDT 106 to each of the ONUs 102 numbering from 1 to n. The above described conventional technique has a second problem, which is that a modulator 108, for converting the common digital service signal input via the digital transmission channel included in the respective paths 107 into the common analog service signal, is required for respective ONUs 102, so that the amount of equipment required increases.